Waves, Light and Sound Study Guide...Unit 1 - Waves References and Notes Work to Submit Study Guide...
Transcript of Waves, Light and Sound Study Guide...Unit 1 - Waves References and Notes Work to Submit Study Guide...
Adult Basic Education
Science
Physics 2104C
Waves, Light and Sound
Study Guide
Prerequisite: Physics 2104 A
Credit Value: 1
Text: Physics: Concepts and Connections. Nowikow et al. Irwin,2002
Physics Concentration
Physics 1104Physics 2104APhysics 2104BPhysics 2104CPhysics 3104APhysics 3104BPhysics 3104C
Table of Contents
To the Student . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vIntroduction to Physics 2104C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vUse of Science Study Guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vRecommended Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Unit 1 - Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1
Unit 2 - Light Properties I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4
Unit 3 - Light Properties II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7
Unit 4 - Sound Properties I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9
Unit 5 - Sound Properties II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 13
Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 17
Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 25
Study Guide Physics 2104Cv
To the Student
I. Introduction to Physics 2104C
This course will introduce you to the nature of sound and light. One way that light appears tobehave is as a wave. (The other way light can behave is as a particle and you will study this inPhysics 3104C). The study of light waves and then sound waves will involve many applicationsof both light and sound.
In addition to your textbook, you will need your scientific calculator. This course, like theprevious courses in Physics does require some understanding of trigonometry. If you have notstudied any trigonometry, you will need to get some extra help on the problems that usetrigonometry.
II. Use of Science Study Guides
Before beginning this course, ensure you have the text and any other resources needed (see theinformation in the Introduction to this course for specifics).
As you work through the Study Guide, you will see that it is divided according to the Units listedin the Table of Contents. When you open a unit it will have the following components:
Study Guide Physics 2104Cvi
To the Student
Reading for this Unit:
Here you will find the chapters, sections and pages of the text you will use to cover the material for this unit. Skim
the sections of the textbook, look at the titles of the sections, scan the figures and read any material in the margins.
Once you have this overview of the unit, you are ready to begin. Do not be intimidated by the content. You will
work through the text, section by section, gaining knowledge and understanding of the material as you go.
References and Notes Work to Submit
This left hand column guides you through the
material to read from the text. Read any
highlighted notes that follow the reading
instructions. The symbols || direct you to
the questions that you should complete when
finished a reading assignment..
You come across three (3) headings in this right hand column.
Writing: This section comprises your notes for the unit.
Here you will find either written questions or
references to specific questions or problems
from your text. You may want to write out
each question followed by the answer. This
material should be checked by your instructor
before moving on to the next unit.
Mathematical problems should have their
solutions checked as you go.
Laboratory: This section indicates if there is a Lab that
should be completed for the unit. Let the
instructor know in advance that you will be
ready for the lab. A lab report should be
submitted for each Lab. Your instructor will
provide guidelines as to how s/he wants the
report written.
Assignment: This section indicates if there is an assignment
that should be completed for the Unit. The
information in the “References and Notes”
column will indicate how you obtain the
assignment. These assignments frequently
relate the science content to technology,
society and the environment.
III. Recommended Evaluation
Written Notes 10%Labs/Assignments 20%Test(s) 20%Final Exam (entire course) 50%
100%The overall pass mark for the course is 50%.
Unit 1 - Waves
Study Guide Physics 2104CPage 1
To fulfill the objectives of this unit, students should complete the following:
Reading for this unit: Physics: Concepts and Connections:Chapter 10: Section 10.1: pages 385-389
Section 10.2: pages 390-393
References and Notes Work to Submit
A mechanical wave is a transfer ofenergy in the form of one or moredisturbances through an elasticmedium. Some terms that you met inSimple Harmonic Motion will apply towaves. A mechanical wave’s energy isproportional to the square of itsamplitude in the same way as that of asimple harmonic oscillator (E = kA )2
Read pages 385 to 389 of Section10.1.||
Writing:
1.1 What is a mechanical wave?
1.2 Explain the difference between a transverseand a longitudinal wave using a Slinky as anexample.
1.3 How are longitudinal and transverse wavescreated on a Slinky?
1.4 How does the particle motion compare to thedirection of the wave’s velocity for a (i)transverse wave and (ii) longitudinal wave?
1.5 What are the two (2) fields that compriselight?
1.6 In what direction do the fields that composelight move with respect to each other and totheir vibrations?
Unit 1 - Waves
References and Notes Work to Submit
Study Guide Physics 2104CPage 2
1.7 What are compressions and rarefactions?
1.8 How are longitudinal and transverse wavesillustrated?
1.9 Explain what each of the following is andindicates its symbol:(a) period(b) frequency(c) wavelength(d) amplitude
1.10 Use a diagram to illustrate each of :(a) amplitude(b) crest(c) trough(d) wavelength
1.11 What mathematical expression relatesfrequency to period?
1.12 What does phase and phase shift mean forwaves?
1.13 Sketch a diagram of a wave whosewavelength is 5 cm and whose amplitude is 2cm. Now below this sketch a phase shift ofë/4 and ë/2 for this wave.
1.14 Complete Questions 1 to 3 on page 389.
1.15 Complete Questions 29 to 30 on page 435.
Unit 1 - Waves
References and Notes Work to Submit
Study Guide Physics 2104CPage 3
Read pages 390 to 393 of Section10.2 || 1.16 What is the wave equation? Explain what
each variable represents.
1.17 What is the electromagnetic spectrum?
1.18 List the seven (7) major regions of theelectromagnetic spectrum.
1.19 What is c and what is its value and units?
1.20 Complete Problems 1 and 2 on page 393.
Unit 2 - Light Properties I
Study Guide Physics 2104CPage 4
To fulfill the objectives of this unit, students should complete the following:
Reading for this unit: Physics: Concepts and Connections:Chapter 10: Section 10.3: pages 394-395
Section 10.4: pages 396-400Section 10.5: pages 400-402Section 10.6: pages 402-404Section 10.7: pages 405-406Lab 10.1: page 442.
References and Notes Work to Submit
Read pages 390 to 393 of Section10.3 ||
Read pages 396 to 400 of Section10.4 ||
Writing:
2.1 What is meant by “rectilinear propagation oflight”?
2.2 For light define: (a) reflection(b) transmission(c) refraction
2.3 In optics, what is (a) a ray, (b) the normal, (c) point of incidence and (d) incident ray.
2.4 In optics, what is a beam?
2.5 Explain the difference between regular (orspecular) reflection and diffuse reflection.
2.6 State the two Laws of Reflection for flatsurfaces.
2.7 What are virtual images?
Unit 2 - Light Properties I
Study Guide Physics 2104CPage 5
References and Notes Work to Submit
Read pages 400 to 402 of Section 10.5||
Read pages 402 to 403 of Section 10.6||
2.8 Describe the five aspects of an image producedin a plane mirror.
2.9 What is lateral inversion?
2.10 Write out the rules for determining how the eyesees an image in a plane mirror (Figure 10.24).
2.11 Complete Question 3 on page 400.
2.12 Complete Problems 48 and 49 on page 437.
2.13 Define refraction.
2.14 What happens to a refracted ray when lighttravels from a less optically dense medium to a moreoptically dense medium? (Use a diagram to illustrateyour answers).
2.15 What happens to a refracted ray when lighttravels from a more optically dense medium to a lessoptically dense medium?
2.16 Complete Question 3 on page 402.
2.17 Complete Question 10(a) and (b) on page 434.
2.18 Define index of refraction.
Unit 2 - Light Properties I
Study Guide Physics 2104CPage 6
References and Notes Work to Submit
Read page 405 of Section 10.7 ||
Check to ensure your calculator is indegrees mode not radians. TryExample 9 to ensure you can use yourcalculator correctly.
Study Example 10 on page 406 ||
Let your instructor know you areready to do Lab 10.1.
2.19 What is the mathematical expression for theindex of refraction? Explain what each letterrepresents.
2.20 Complete Problems 1 and 2 on page 404.
2.21 Express Snell’s Law in (a) words and in (b) amathematical expression.
2.22 Complete Problems 62 and 63 on page 438.
2.23 Complete Problem 1 and 2 on page 407.
2.24 Complete Problem 2 on page 407.
Laboratory:
Complete and submit Core Lab #1: Lab 10.1: Snell’sLaw on page 442.
Unit 3 - Light Properties II
Study Guide Physics 2104CPage 7
To fulfill the objectives of this unit, students should complete the following:
Reading for this unit: Physics: Concepts and Connections:Chapter 10: Section 10.8: pages 408-409
Section 10.9: pages 411-413Section 10.10: pages 414-418Section 10.11: page 419Section 10.12: page 424-429Section 10.13: pages 429-430
References and Notes Work to Submit
Read pages 411 to 413 of Section10.9. ||
Writing:
3.1 What is total internal reflection of light?
3.2 Explain why light is an efficient means oftransferring information.
3.3 What is a critical angle?
3.4 Why does total internal reflection only occur forlight travelling from a more dense medium to a lessdense medium?
3.5 List 5 examples of the use of fibre optics forinformation transfer.
Unit 3 - Light Properties II
Study Guide Physics 2104CPage 8
References and Notes Work to Submit
Read “The Rainbow,” on pages 414to 415 in Section 10.10 ||
Read pages 424 to 425 of Section10.12 and Study Figures 10.70 and10.71 on page 426. ||
You may want to use the processdescribed in Figure 12.3 on page 487to help you solve Problem 90.
3.6 Explain how the rainbow colors are produced.
3.7 What is the principle of superposition?
3.8 Explain (using a diagram) the differencebetween constructive and destructive interference.
3.9 What is meant by phase shift?
3.10 What are maxima?
3.11 What are nodal lines?
3.12 Complete Problem 90 on page 440.
Unit 4 - Sound Properties I
Study Guide Physics 2104CPage 9
To fulfill the objectives of this unit, students should complete the following:
Reading for this unit: Physics: Concepts and Connections:Chapter 11: Section 11.1: pages 445-449
Section 11.2: pages 450-453Section 11.3: pages 453-458Section 11.4: pages 458-461Section 11.5: page 463Section 11.6: pages 468-470Section 11.7: pages 471-473Lab 11.2: page 483
Study Guide Appendix B
References and Notes Work to Submit
Read pages 445 to 448 of Section 11.1||
Read the information in Question 1 onpage 449 ||
Writing:
4.1 What is simple harmonic motion?
4.2 What type of wave are produced in strings ofmusical instruments?
4.3 What type of waves are sound waves?
4.4 Referring to Figure 11.4, explain why waterwaves are complex waves.
4.5 What is the wave equation? Explain what eachvariable represents.
4.6 Complete Problems 1 to 3 on page 449.
4.7 Explain how animals use echolocation (sonar)to locate objects.
Unit 4 - Sound Properties I
Study Guide Physics 2104CPage 10
References and Notes Work to Submit
Read pages 450 to 452 of Section 11.2||You are not responsible for solvingproblems involving Mach Numbers.
Read pages 453 to 457 of Section 11.3||
You may want to use the glossary atthe back of the text for definitions.
4.8 Describe the three factors that affect the speedof sound.
4.9 Explain what the terms (a) compression and (b)rarefaction mean.
4.10 Explain how sound is transmitted to anotherperson.
4.11 What is the mathematical expression for theeffect of temperature on the speed of sound in air?
4.12 Complete Questions 1 to 3 on page 453.
4.13 What is a Mach Number?
4.14 Explain what each of the following mean (a)subsonic, (b) supersonic (c) hypersonic.
4.15 What is the sound barrier?
4.16 Explain how a sonic shock originates.
4.17 Define acoustic pressure.
4.18 Explain why supersonic travel is prohibitedover North America.
4.19 What types of sound speeds are associatedwith a sonic boom?
4.20 Complete Question 3 on page 458.
Unit 4 - Sound Properties I
Study Guide Physics 2104CPage 11
References and Notes Work to Submit
Inform your instructor you are readyto complete Core Lab #2.
Submit the completed lab report forevaluation.
Read pages 458 and 459 of Section11.4 to the end of Example 7 ||
Assume for problem 50 that “closeproximity” means 1 m.
Read from “Decibel System” on page459 to end of page 461. ||
Read page 463 of Section 11.5 ||
Read pages 468 to 470 of Section 11.6and Appendix B. ||
Laboratory:
Complete and submit the report for Core Lab #2:Speed of Sound on page 483.
Writing:
4.21 Define intensity.
4.22 What is the mathematical expression for soundintensity. Explain what each variable represents.
4.23 Complete Problems 49 and 50 on page 479.
4.24 What is the mathematical expression for thedecibel unit of sound intensity?
4.25 Complete Problems 1 and 2 on page 462.
4.26 What is the Doppler effect?
4.27 Explain how the Doppler effect arises.
4.28 Complete Question 1 on page 467.
4.29 Explain the role of the outer, middle and innerear in our ability to hear.
4.30 How do loud bursts of noise damage ourhearing?
4.31 What frequency range can we hear?
Unit 4 - Sound Properties I
Study Guide Physics 2104CPage 12
References and Notes Work to Submit
Read page 471 of Section 11.7 ||
4.32 To what frequencies are our ears mostsensitive?
4.33 Are we more sensitive to high pitch or lowpitch frequencies?
4.34 Define the terms infrasonic and ultrasonic.
4.35 Explain how sonar functions.
Unit 5 - Sound Properties II
Study Guide Physics 2104CPage 13
To fulfill the objectives of this unit, students should complete the following:
Reading for this unit: Physics: Concepts and Connections:Chapter 12: Section 12.1: pages 486
Section 12.2: pages 486-489Section 12.3: pages 489-491Section 12.4: pages 491-492Section 12.5: pages 494-496Section 12.7: pages 505-507Section 12.8: pages 508-510
Study Guide Appendix A - “The Physics of Guitars”
References and Notes Work to Submit
Read pages 486 to 488 of Section 12.1and 12.2 ||
Writing:
5.1 Why are longitudinal sound waves illustrated astransverse waves?
5.2 Define interference.
5.3 What is the principle of superposition?
5.4 Use Figure 12.3 to write a summary of applyingthe principle of superposition.
5.5 Complete Problem 10 on page 515.
Unit 5 - Sound Properties II
Study Guide Physics 2104CPage 14
References and Notes Work to Submit
Read pages 489 to 491 of Section 12.3||
Read pages 491 to 492 of Section 12.4||
Read pages 494 to 495 of Section 12.7||
Read pages 505 to 507 of Section 12.7||
5.6 Explain what is meant by the following asapplied to sound waves:
(a) absorption(b) transmission(c) reflection
5.7 What happens to sound waves as they movefrom a slower to a faster medium?
5.8 Define standing wave (see glossary).
5.9 Explain what each of the following terms mean:(a) nodes(b) antinodes(c) internodal distance
5.10 If there are five (5) nodes, how manyinternodal distances exist?
5.11 Complete Question 1 on page 494.
5.12 What is mechanical resonance?
5.13 Describe how mechanical resonance resultedin the collapse of the Tacoma bridge.
5.14 Explain what is meant by each of the followingterms: (a) pitch (b) loudness (c) quality.
Unit 5 - Sound Properties II
Study Guide Physics 2104CPage 15
References and Notes Work to Submit
Read pages 508 to 510 of Section 12.8||
Loud speaker interference occurs inspace - that is if you have two loudspeakers parallel to each other, therewill be places where the sound is veryloud (constructive interference ) andother places with destructiveinterference where the sound is verylow or there is no sound at all.
Beats involve interference in time.Sound level rises (constructiveinterference) and falls (destructiveinterference). The regularly spacedintensity changes are called beats.
Read Appendix A ||
5.15 Explain how interference causes interestingeffects in the case of: (a) side by side speakers and(b) beat frequency.
Assignment:
Complete and submit the Questions 1 to 4.
Appendix A
Study Guide Physics 2104CPage 19
The Physics of Guitars
Outcomes:1. To describe and evaluate the design of technological solutions and the way they function, using
scientific principles. 2. To analyze natural and technological systems to interpret and explain their structure. 3. To analyze and describe examples where technological solutions were developed based on
scientific understanding. 4. To analyze society's influence on scientific and technological endeavors. 5. To analyze why and how a particular technology was developed and improved over time. 6. To analyze and describe examples where scientific understanding was enhanced as a result of the
invention of a technological device. 7. To describe what is meant by a vibration, and give examples from technology.8. To explain how standing waves are produced on a stretched string.9. Given the fundamental frequency and fundamental wavelength of a vibrating string, produce
diagrams of various overtones labelled to show wavelength and frequency of each.10. Describe how sound as a form of energy is produced and transmitted.
Introduction
Chris Griffiths of St. John's, Newfoundland has had
a lifelong interest in music, beginning guitar lessons
at the age of twelve. He began building guitars at
the age of seventeen. Since then he has turned his
interest into the successful guitar making business
known as Griffith's Guitar Works - a 20 000 square
foot, multimillion dollar high tech acoustic guitar
factory. Though Griffiths may not have chosen
physics as a career, a knowledge
of physics was certainly important
in producing great sounding
guitars like his latest creation - the
Garrison. The Garrison guitar line
includes a full range of acoustic
guitars, beginning with the G-10
and following through to the top
of the line G-50. Through
innovative construction
techniques, these guitars offer
"superb playability and clarity of
tone" that is setting a new
standard for acoustic guitars
(Garrison Guitars).
Construction
There are many different types of acoustic guitars,
producing varying qualities of sound. However they
all share some basic construction features. The three
main parts of any guitar are the hollow body, the neck
and the head.
Body
The guitar body includes the soundboard, a wooden
piece mounted on the front of the guitar. The
soundboard should be made so that it can vibrate up
and down relatively easily. It is usually made of
spruce or another light springy wood. Griffith's
Garrison guitars are constructed from all solid wood
including East Indian rosewood, sapele, englemann
spruce, sitka spruce, Canadian birch and western red
cedar. There is a large hole in the soundboard called
the sound hole. Also attached to the soundboard is
the bridge. The bridge anchors one end of the six
strings. On the bridge is a saddle which the strings
rest against.
Study Guide Physics 2104CPage 20
When the strings are plucked they vibrate. The
vibrations travel through the saddle and bridge to
the soundboard. The hollow body of the guitar then
amplifies the vibrations of the soundboard. These
vibrations then disturb the air producing a sound
wave reaching our ears. Without the amplification
of sound produced by the hollow body, these
vibrations would be barely audible. Bracing refers to
the internal reinforcement of a guitar that must add
strength where necessary but still allow the top to
vibrate as freely as possible. Garrison guitars boast a
single-unit brace that allows the resonant sound to
travel uninterrupted through the guitar no matter
where the vibration is created.
Neck
The neck of the guitar joins the body to the head.
On the face of the neck (called the fingerboard) are
metal pieces called frets that are cut at specific
intervals. When a string is pressed onto a fret, the
length of the string is changed. Changing the length
changes the sound that is produced. The frequency
of sound produced is inversely proportional to
Llength (f % / ). As length decreases frequency1
increases. The six strings on guitars also have
different weights which affect the sound produced.
The first string is as fine as a thread while the sixth is
wound much heavier and thicker. More massive
strings vibrate more slowly. The frequency of sound
produced is inversely proportional to the square root
of the density of the string . As the
density decreases the frequency increases. The
frequency is also inversely proportional to the
diameter of the string . This means that as
the diameter decreases, the frequency increases.
The strings themselves do not make much noise
when plucked since they do not cause a large
disturbance to the air around them. It is the
vibrations of the bridge and body that produce such
pleasing sounds.
Head
Joining the neck to the
head is a piece called the
nut. The nut has grooves
to hold the strings. From
the nut the strings are
connected to the tuning
pegs on the head.
Turning these pegs
allows the tension in the
strings to be increased or
decreased. These pegs
are used to tune the guitar. The tighter the string the
higher the pitch and frequency of sound produced. In
fact, frequency varies directly as the square root of
the tension .
Electric Guitars
The major difference between electric guitars and
acoustic guitars is in the body. Electric guitars have
a solid body with no sound hole. A string plucked
on an electric guitar makes almost no sound if not
connected to an amplifier. This is because without a
hollow body there is nothing to amplify the sound.
Electric guitars therefore rely on amplifiers and
speakers to produce sound. Vibrations are sensed
electronically and then sent to the amplifier and
speaker.
Theory
Standing Waves
Guitar strings are fixed on both ends by the saddle
and the nut. The body of the guitar will resonate
when standing waves are set up on the strings. A
string will resonate when its length is equivalent to
½ë, ,ë,3/2ë, 2ë, etc. This is the same pattern
of resonant lengths that exist in an open air column.
The standing waves in the strings are illustrated in
the following diagrams.
Study Guide Physics 2104CPage 21
Note that since the string is fixed at both ends, any
vibration of the string will have nodes at each end.
This limits the possible vibrations that can be
achieved on a given length of string. We can see
that for each of the diagrams, the wavelengths are
32L, L, / L and ½ L. In general this is written as2
where n is the harmonic number. Thus
for each standing wave pattern, the frequencies are as
follows (where v is the speed of sound):
Harmonic:
Since all waves in the same string travel with the
same speed, then waves with these different
wavelengths must have different frequencies. The
1 1 1 1frequencies f , 2f , 3f , 4f , etc. are referred to as the
harmonic series. It is the rich variety of harmonics
that make a guitar or any stringed instrument
interesting to hear.
Conclusion
Guitar construction is really a combination of art
and science. Physics principles dictate the kind of
sound produced in terms of frequency and
wavelength. However it is the craftsman's artistry in
constructing the shape of the body and soundboard
that give each guitar its distinctive sound. For
Griffiths there has been a "brilliant blend of
technology, art and craftsmanship" which has set a
new standard for acoustic guitars worldwide.
Questions
1. A guitar string of length 0.60 m has a frequency
of 395 Hz. If the string is shortened to 0.30 m,
what is it's new frequency?
2. A standing wave is set up on a guitar string of
length 0.60 m. If the string vibrates in the third
harmonic, what is the wavelength of the sound
produced?
3. What is the main function of the body of the
guitar in producing the music we hear?
4. A guitar string has an original tension of 146 N.
How would the tension have to change to have
the string vibrate with a frequency of 292 Hz?
5. Research: How has Griffith's guitars upped the
Study Guide Physics 2104CPage 22
standard for worldwide acoustic guitar construction?
References
Dick, G., Geddis, A.N., James, E., McCaul, T.,McGuire, B., Poole, R., & Holzer, B. (2001).Physics 11. Toronto: McGraw-Hill Ryerson..
Garrison Guitars. Available:http://www.garrisonguitars.com.
Griffith's Guitar Works. Available:http://relay.acadiau.ca/fps/business/aics/highsch/griffith.htm
How Guitars Work. Available:wysiwyg://23/http://www.howstuffworks.com/guitar1.htm
How does a guitar work? Available:http://www.phys.unsw.edu.au/music/guitar/intro_engl.htm
News Release. (2001). Available:http://www.gov.nf.ca/releases/2001/indrural/0926n02.htm
Nowikow, I., & Heimbecker, B. (2001). Physics:Concepts and connections. Toronto: IrwinPublishing Ltd.
The Guitar. Available:http://www.bsharp.org/physics/stuff/guitar.html
Study Guide Physics 2104CPage 23
ActivityActivity:
Purpose: To experimentally determine whether the soundboard really amplifies sound.
Materials: large bowl C tape
C plastic wrap C rubber band
Procedure:
1. Tightly seal a large bowl with plastic wrap (you may need to use tape to wrap the plastic tightly to the
sides).
2. Tape a rubber band to the center of the taut plastic wrap and twang the rubber band.
3. Compare the sound heard to the twang of an identical rubber band not taped to the plastic wrap. You should
notice a big difference. The plastic wrap greatly increases the amount of surface area that is vibrating, so the
sound is much louder. (This activity is taken from the web site “How stuff works”
http://www.howstuffworks.com/guitar1.htm)
4. Demonstrate how to produce standing waves for students. A very effective way to do this is to attach one
end of a string to an electric drill, and the other securely to some immovable object. When the drill is turned
on at varying speeds, students can clearly see standing waves at the fundamental frequency and various
overtones.
5. Refer to the activity at the following web site for an activity on making standing wave patterns on a
Appendix B
Study Guide Physics 2104CPage 27
Hearing Loss
Some people lose their hearing ability in their 30s and 40s. One out of 5 adults and morethan half of all people over the age of 80 have hearing loss. Age related hearing loss is calledpresbyacusis. Presbyacusis generally involves the loss of ability to hear high frequency soundsfirst. This involves difficulty to hear speech sounds with consonants such as s, t, k, p and f.
This hearing loss generally occurs due to problems with the inner ear, usually due todamage to the tiny hair cells in the cochlea. Once damaged these hair cells cannot be repaired orreplaced. As people age they gradually lose these hair cells, resulting in a gradual hearing loss.
Hair cells however can also be damaged by excessive noise. When ears are exposed tohigh intensity noise due to either a work environment or to listening to loud music, hearingimpairment can results. For this reason, ear protection devices should be worn in workingenvironments where there is loud noise. Young people in particular should be careful as to howloud is music they listen to.
Other reasons for hearing loss involves having been exposed to diseases such as mumps,meningitis, multiple sclerosis or to certain drugs such as quinine, or some antibiotics such asstreptomycin and gentamicin. Hearing loss can occur in an infant if the mother is exposed toGerman measles (rubella) while she is pregnant. It can also occur due to head or ear injuries.Sometimes hearing impairment can be inherited.
Some people can use technology to overcome hearing loss. Hearing aids work for somepeople and for others surgery can be used to treat the problem.